fatty acid beta-oxidation

Saturday 19 July 2003

Definition: Acyl-CoA dehydrogenases (ACADs; EC 1.3.99.13) are mitochondrial enzymes that catalyze the initial rate-limiting step in the beta-oxidation of fatty acyl-CoA. ACAD9 belongs to a group of ACADs that act on fatty acids containing 14 to 20 carbons.

Beta oxidation is the process by which fatty acids, in the form of acyl-CoA molecules, are broken down in the mitochondria and/or in peroxisomes to generate acetyl-CoA.

Mitochondrial fatty acid beta-oxidation is one of the main energy-producing metabolic pathways in eukaryotes through the entry of acetyl-CoA into the Krebs cycle.

Fatty acids are oxidized inside the mitochondrial matrix but the fatty acids to be oxidized come from the cytosol.

Fatty acids are activated in the cytosol by esterification with Coenzyme A (CoA) to form acyl-CoA (RCO-CoA, where R is the fatty acid acyl group).

Activated medium-chain fatty acids (C8 fatty acid and C10 fatty acid) freely diffuse into mitochondria to be oxidized but long chain fatty acids do not diffuse into mitochondria so they must be transported in.

The transport of long chain fatty acids into mitochondria for oxidation is accomplished by the carnitine palmitoyltransferase system (CPTI and CPTII).

CPTI exchanges carnitine for the CoA attached to long chain fatty acids to form a fatty acid-carnitine conjugate (RCO-carnitine).

The fatty acid-carnitine is transported into the matrix by a transporter protein in the inner mitochondrial membrane. Once the fatty acid-carnitine is inside the matrix, CPTII exchanges CoA for carnitine to produce fatty acid-CoA once again, ready to enter fatty acid oxidation in the matrix to produce energy.

The free carnitine is transported back out to renew the cytoplasmic pool of carnitine and allow the transfer process to continue. (From Biocarta)

Acyl-CoA dehydrogenases (ACADs) (EC 1.3.99.13) are mitochondrial enzymes that catalyze the initial rate-limiting step in the beta-oxidation of fatty acyl-CoA.